EAST COAST RAILWAY

Evening Post, Volume CXXV, Issue 149, 27 June 1938, Page 12

EAST COAST RAILWAY

PROGRESS MADE

TUNNELLING MACHINERY

Recording the progress made in tunnelling on the Waikokopu-Gisborne section of the East Coast railway, the "Poverty Bay Herald" gives the following distances pierced:—

Waikara Tunnel, 72 chains.—North;rn face: Top heading, 1184 ft; full secion, 1118 ft; concrete lining, 7301t. Southern face: Top heading, 738 ft, ull section, 669 ft; lining, 201 ft. Coast Tunnel, 46 chains.—Bottom leading completed from end to end; inlargement to full section proceedng. , . Tikiwhata Tunnel, 149 chains.-— Northern face: Top heading, 945 ft; :ull section, 914 ft; lining proceeding. Southern face: Top heading, 627 ft; full lection, 594 ft; lining, 495 ft. The above figures represent progress nade to date on the major tunnelling obs which represent the key positions >n the Waikokopu-Gisborne section of ;he construction of the Gisbornetfapier railway. Numerous smaller tunnels have been carried at least half-way to comaletion, so far as the excavation is :oricerned, and in the aggregate more than a mile and a half of tunnelling work has been completed to date on this line. Mechanical equipment has brought about a revolution in the hitherto extremely arduous work of the gangs, and speeded up progress amazingly, [ts introduction is no less important, in its bearing on the skilled work of tunnelling, than the introduction years ago of the compressed-air drill which took the grunt out of blasting preparations. SAVING MANUAL WORK. By the employment of a device known as a scraper, weighing between five and six tons and operated by electric power, manual handling of spoil from the tunnel face has been almost entirely eliminated in the two jobs on which full-section excavation has been instituted. The scraper has the same general features as a dragline scoop, with the difference that it requires no boom. A pulley-block is secured close to the face of the tunnel, and through it runs a steel cable, by means of which the scoop is drawn out for filling. The operation of controls on the power unit reverses the movement of the scoop, and it is drawn, fully loaded, to the ramp of the scraper. Climbing this ramp it discharges its load into trucks which have been run under it in readinCTwo or three trips of the scoop, made in a minute or less, will fill a yard and a half truck with small debris. One trip is sometimes -sufficient, for the scoop will lift a rock large enough to fill a truck, and that without trouble. Under the old system of working spoil, such rock would have to be broken down to the lifting capacity of two men. The scraper makes light of them. All that unskilled manual labour can do for this machine is to put the spoil in the track of the scoop. FULL-SECTION TUNNELLING. The full-section method of constructing tunnels, evolved in the United states and long' practised there and in Canada, had not been tried in railway tunnel work in New Zealand before its adoption for the East Coast Main Trunk section from Waikokopu to Gisborne. Its merits are being realised, more and more as the work proceeds. It calls for _an accurate use of specially-cut timbering, a job not at all beyond the capabilities of New Zealand tunnellers, who take pride in their good standing among the best of their craft in the world. It allows for the use of such mechanical aids as the scraper, and facilitates the ' early application of the concrete lining which finishes the tunnelling job. How important this advantage is to the progress of work is illustrated in the case of the Waikara tunnel, in which the advanced face is 1184 feet from the northern portal, with the tunnel opened out to its full section for 1118 feet, and the concrete lining already applied for 730 feet. The older method, which was standard practice with the Public Works Department until recently, depended upon the opening up of the bottom heading for the full length of the tunnel, after which the top heading was broken out and the shaft enlarged to its full dimension, preparatory to lining with concrete. This method has been used in all the smaller tunnels on the Waikokopu-Gisborne section, including the 46 chains coast tunnel. It has only been displaced where a huge job of excavation makes possible the economic employment of the latest mechanical aids.